Diesels challenge hybrids for efficiency, low emissions

Not too long ago the car makers where competing with each other on performance—mainly measured by horsepower and acceleration. Fuel economy did not have high attention in the benchmarks for premium cars. This has changed recently and fuel economy is suddenly a major trait that every OEM has on its list.

This trend was not only driven by environmental regulations of various governments but the fuel price itself. Also consumer behaviors have changed a lot and our society is undergoing a paradigm change with regards to our transportation concepts and mobility behavior.

These days more and more new car customers are looking at the datasheets and specifications for fuel consumption and emissions. The prestige and image of many cars are now largely driven by its benchmark fuel efficiency and emission values rather the pure horsepower backed driving performance and acceleration. So this changing consumer behavior and the strong government involvement via rules, regulations and incentives for environmentally friendly cars leads the automotive market towards a new generation of cars to satisfy this trend of “green transportation”. And that’s the main reason why hybrid-electric Vehicles (HEVs) are showing up in every fleet and product line of the major car manufacturers.

What we often forget, especially here in the U.S., is that fuel efficiency and low emissions are not only achieved via revolutionary game-changing technologies like the emission-free electric powertrain of a hybrid vehicle. Looking at the fuel efficiency of currently available or shortly announced HEVs, you would be surprised that this fuel efficiency can be pretty closely matched by a modern diesel engine using state-of-the-art direct fuel injection systems and an electronically controlled and well optimized motor control unit. The big difference comes with the price "bump up" for the technology that the buyer pays.

A diesel engine typically adds only moderat cost compared to a comparable gasoline engine (in the range of approximately $1-2,000). The price adder of HEVs vs their traditional standard combustion engine version is normally at least 2-3 times as high. The reason for this is that hybrid-electric vehicles need to incorporate a complete electric powertrain plus all the energy management and storage systems, a high voltage battery, and plenty of electric systems like inverter, converter, and charger applications into the vehicle architecture.

Therefore the additional electronic content in a HEV is much higher than the little electronics in the motor control unit plus some diagnostic and monitoring sensors which are needed to build a very efficient direct fuel injection system for a modern diesel aggregate in a much more cost effective way.

Checking the numbers
Let’s look at the table below, which shows the average highway fuel consumption in miles/gallon of HEVs vs diesel. There is not much difference between similar sized and powered diesel and HEV cars. The emission values of those cars are also in a comparable range. Only the pure city consumption of the HEVs seems to be superior since the HEV-engine typically shuts down (so called start-stop mode) every time the car is stopped in a traffic jam or at red lights. But adding relatively low cost start-stop functionality to a regular diesel engine (so called micro-hybrid) would push the diesel city mileage likely into the same range as the one advertised for gasoline-HEVs.

Looking at these numbers the diesel solutions could offer quite some threat to the penetration of HEVs. In countries in Europe where diesel is a well established engine type and the consumer acceptance is at least as high for gasoline powered aggregates we see already a very strong market penetration of diesel while HEVs seem to sell much harder compared to U.S. or Japan, for example.

This is certainly quite a surprising data to me. Who knew that the old diesel engine could be comparable to hybrids in terms of fuel efficiency. A driver that is looking to save money on fuel costs in the long term will certainly take this into account. Still, the amount of emissions that a diesel engine emits is largely over a hybrid engine, so in a way, hybrids are still better.
Peter - http://www.pmwltd.co.uk/

Get your facts straight first. Current new diesels are extremely low in emissions now 2011 are availabe from many manufacturers with low sulfur diesel or biodiesel it is much easier now to meet the emissions. most manufacturers have met the federal requiremnts years ahead of schedule in order to meet the stricter Cal. requirements. I agree it is rather stupid to require older vehicles to comply with standards that they were not designed to meet. Diesel hybrids
would require much smaller diesel engines since acceleration could be from battery power and diesel power combined and then recharge when power is not needed. Box trucks could be powered from a small direct injection turbodiesel. California is a bit out of hand with their emissions laws. They seem to mandate things that are difficult to achieve but then the rest of the country does not have a legendary smog problem as they do.

i would think that you also need to include the mass of waste per mile in the calculation. A lightweight hybrid that is scrap metal after 100,000 miles or a solid diesel that is still working just fine at 300,000 miles are going to be different in the amout of total pollution generated per fucntional passenger mile.
The total energy bill, of manufacture, operation and disposal should be considered when looking at efficiency of the car as a system.

@Majestek: "More fuel burned = more emissions", sorry but this is not true. Quality of fuel and combustion type are way more important factors. And care has to be taken when speaking generally of "emissions". One thing is C02 emission, which is heavily (but not exclusively) linked to the amount of fuel burned; one other thing are pollutant emissions, which are higher in diesel engines, no matter how you measure it. A typical gasoline car has no particulate emission whatsoever, and HC/CO/NOx are quickly removed with a catalitic converter, while diesel engines require expensive exhaust treatment, subjected to maintenance and failures, and still leak some particulate. Moreover, while CO2 emissions are size-dependent, this is not the case for pollutant emissions: a recent huge SUV may well have lower pollutant emissions of an older compact.

@ Steve Ravet. You can't look blindly on the data. It may appear that diesel has higher emissions. But consider this. As others I drive the TDI Jetta. I manage to make a tank last two weeks before fill-up commuting to work. I would use twice the amount of gas which would cost me twice as much and I would burn up twice as much fuel. See where I'm going? More fuel burned = more emissions.
I see two problems with the way we "quantify" things.
1. MPG is ok but it needs to be more like MilesPerDollar/Gallon.
2. When comparing emissions MPG should be taken into consideration

@nando basile: Autonomy? You have poor information. HEV's don'T EVER need to be plugged in. You simply put gas in like any other car. With my commute, I travel about 500 miles/week in my civic hybrid. I put about 10.5 gallons on Monday's. I also occasionally drive from SF to Mesa, AZ to work on our rental. Almost 800 miles. I have to stop for a body break more than to get gas (one gas stop does the trick for my 12+ hour trek).

I have to disagree with the author on one fundamental point. The city driving advantage is due to recovering the energy during the stop, not from stopping the engine. Simply shutting off the engine at stop signs is likely to provide marginal benefit. If you calculate the energy used to accelerate, being able to recover that dwarfs other effects.

What has held diesels back, at least here in California, is not prejudice, but emissions. When diesels can meet California's strict emissions standards, then they will be sold in the state. Until then, they can't be sold here. No prejudice--just cold hard numbers. Their are a few cars that now meet this and more are coming.
What about an HEV powered by a diesel engine?--roldan
Great idea. Haven't they been doing that with trains for decades now?